1. Field of the Invention
The present invention generally relates to a warning device for vehicles which serves the purpose of promptly warning a driver of an object that approaches the vehicles.
2. Description of the Prior Art
Conventionally, such a warning device for vehicles has been proposed in order to provide for safe driving of the vehicle, and thus prevent possible accidents and the loss of properties and human lives. In such a conventional device, an infrared light-emitting diode is disposed at one side of the vehicle. As a current is intermittently supplied to the diode, an infrared light is emitted. When an object approaches the vehicle, the infrared light is reflected, and this reflected wave is received by a receiving diode. Then, a signal from the receiving diode is amplified by means of inverting and non-inverting differential amplifiers, and thereafter rectified. This rectified output is applied to an inverting differential amplifier, so that a voltage with a proper DC level is generated. As this generated voltage actuates the transistor, an LED is lit. At the same time, a warning from a melody speaker is generated by a melody generator, so that the driver can promptly recognize that an object is approaching the vehicle.
However, such a warning device may malfunction due to infrared lights contained in the sun light or generated from remote controllers for household electrical appliances. Thereby, there is a problem of lowered reliability of the warning device. Even when an object is close to the vehicle, about which the driver has to promptly take an action, such as a stop action, a warning melody is generated constantly, so that the driver may not recognize such condition immediately. Thereby, there is a problem of a possibility of causing accidents.